Recently, resin molded articles used in automobiles, home electric appliances, construction materials and so forth are often manufactured by a lamination (multilayer molding method) by fusion bonding integrally a skin material having a resin decorative layer to a core material composed of a thermoplastic resin in order to improve the quality of a molded article and add a value thereto by providing an article with decorativeness, good feeling of touch and the like, and to reduce a cost by omitting some steps in the molding processes.
The technology described in JP-A-59-150740 for “Method for Manufacturing Multilayer Molded Article” discloses a typical molding method for laminating a skin material to a core material. That is, disclosed in the conventional art is such that after the peripheral portions of a skin material are holded between a skin material fixing frame, which is movably attached to a female mold and has an opening through which a male mold slidingly passes, and the male mold, a resin melt is supplied to the space between the skin material and the male mold, and the skin material is laminated integrally to a core material fromed from the resin melt by clamping the male mold and the female mold.
Further, there are proposed various methods for manufacturing a multilayer molded article laminated with a skin material having a good feeling of touch and free from any damage. Among these conventional arts, there is given illustratedly a method disclosed in U.S. Pat. No. 5,154,872 under the title of “Process for Producing Multilayer Molded Article” in which much attention has been paid to the conditions for supplying a resin melt for a core material. According to the method disclosed therein, the clampling of a male mold and a female mold is started, and then a resin melt for a core material is supplied to the space formed between a skin material and the male mold with keeping the cavity clearance between the male mold and the female mold in the range of 5-100 mm, during a state that the mold clamping action is temporarily stopped in the midway of the mold clamping action or that a mold clamping rate is set to 30 mm/sec or less. This method is a method of fusion bonding the skin material and a core material using a vertical mold clamping type press molding machine.
When this conventional art is applied as it is to a horizontal mold clamping type injection molding machine (or press molding machine), there remain following problems unsolved. That is, when a resin melt is injected into the cavity of the mold and the cavity is filled with the resin melt in a state that the mold is opened larger than a specific distance, for example, at least 50 mm, the resin melt injected into the cavity hangs down by the influence of gravity. As a result, a multilayer molded article having good feeling of touch cannot be effectively manufactured due to the fluctuation in the wall thickness of the molded article caused by the resin melt filled unevenly, the occurrence of burrs caused by the invasion of the resin melt into the parting face and the landed part of the mold, and the like.
Further, if one tries to form a laminated molded article by using a horizontal mold clamping type injection molding machine without using the a material fixing frame or the like, the skin material does not get into the cavity of the mold even if the resin melt is filled into the cavity under the above-mentioned state. Even if the mold is closed in this state, the skin material is partly in excess in the mold since the skin material is not changed into a shape corresponding to a molded article. Thus, even if the mold is filled with a resin melt for a core material, the excessive portion of the skin material is heated and drawn, and resultantly wrinkles are formed on the skin material, thereby the appearance of the surface of the skin material is greatly deteriorated.
Further, when the injection and filling-up of a resin melt is carried out by placing the mold in a state in which no hanging-down of the resin melt is caused, that is, in a state that the mold is opened, for example, at a distance of about 5 mm not so as to cuase the hanging-down of the resin melt injected, a problem arises in that the skin material is melted and damaged in the vicinity of gate portions due to high temperature of the injected resin melt.
As described above, when the lamination is carried out using the horizontal mold clamping type injection molding machine, it is necessary to solve the hanging-down problem of an injected resin melt as well as to prevent the damage of a skin material in the vicinity of gate portions. However, these problems cannot be solved by the conventional molding method.